Slow-release coating composition consiting of wax and ethylene vinylacetate



. Richard C. Fox, San Rafael, Califi, assignor to Chevron ResearchCompany, a corporation of Delaware No Drawing. Filed Sept. 28, 1964,Ser. No. 399,855

3 Claims. (Cl. 71-64) This invention relates to slow-release particles,more particularly, it relates to particles which comprise a water-.soluble substance coated with wax-resin mixtures that allow theregulated slow dispersal of the materials into the soil, etc.

With the advent of modern agricultural methods and the increased use ofchemical fertilizers, it has become apparent that the development ofmeans to allow the regulated dispersal of plant nutrients and othermaterials such as weed killers, etc., is of great importance. Areas ofparticular interest for such products are in the raising of specialcrops, for example in gardening, planting of forest seedlings, plantingnurseries and in home lawns. In each of these cases, it is highlyimportant that the fertilizers be distributed evenly, in order that theynot be burned by the excessive application to roots, stems and leaves offertilizer. Additionally, the regulated dis persal allows singleapplication of fertilizer which will last for long periods of time, andrequiring less labor. Geographically, such means are of particularinterest where rainfall is heavy and depletion of the soil due toleaching is thus high.

Various means have been proposed to effect the slowrelease of nutrients,etc. Efforts have been made toward altering the physical and chemicalstructure of the nutrients themselves. For example, the solubility ofthe nutrient materials has been reduced in order to inhibit release.Further, the chemical structure of the nutrient has been altered inorder that slow-release may be effected. Examples of this approachinclude the use of urea-formaldehyde nitrogen compound and variouschelated materials as fertilizers. Of late, considerable interest hasbeen directed toward means of coating and coating materials for nutrientparticles which will retard release and thus prevent rapid leaching.

Numerous coating materials and methods of application have beenemployed, and efforts to obtain satisfactory controlled release ofnutrient material have been made. Among the coating material employedhave been petroleum waxes, various chemical resins, asphalt, etc.However, numerous disadvantages have been encountered in the use of mostof these materials. Such disadvantages include high cost of material,the inability to provide complete coating or the escape of nutrientmaterial recently recorded, etc.

It has now been found that highly regulated slow-dispersal of variousmaterials can be provided by a slowrelease material which is awater-soluble particulate body having a uniformly distributed coating onsaid body comprising a mixture of 25-95% by weight of wax and from 5-75%by weight of a resinous material selected from the group consisting of(a) a copolymer of an unsaturated ester containing a total of from 3 to7 carbon atoms with olefins of 2 to 4 carbon atoms, and (b) polymers andcopolymers of olefins having from 2 to 4 carbon atoms and wherein saidresinous materials have a molecular weight of at least 10,000. Byuniformly distributed is meant that at least 80% of the particulatebodies are completely covered with the coating composition. The coatingscomprise from 2 to 25% by weight of the slowrelease material. Weights offrom 5 to 15% are preferred.

Waxes suitable for use in the coating of this invention i ted StatesPatent 3,372,019 Patented Mar. 5, 1968 include paraflin waxes andmicrocrystalline waxes. Paraffin wax is defined as a solid, crystalline,hydrocarbon mixture wholly derived from that portion of crude petroleumcommonly designated petroleum distillate; or from hydrocarbon synthesisby low temperature solidification and expression are by solventextraction. It is solid at room temperature, and deforms at thistemperature only relatively slightly, even under considerable pressure,and has a low viscosity (35-45 SSU) at 200 F. when melted.Microcrystalline waxes have molecular weights of from 400-700 andaverage molecules of 40 to 50 carbon atoms.

They contain a large proportion of side chains and a sizable number ofcyclic in it.

Examples of particular resins which may be suitably employed arecopolymers of ethylene with ethylacrylate, copolymers of ethylene withvinyl acetate. Example of suitable homogeneous polymers includepolyethylene, polypropylene, polymers of 4-methyl-pentene-l, etc. Theresins should have a molecular weight between 10,000 and 2,000,000. Therange of 20,000 to 500,000 is preferred.

The coating material may be applied to the watersoluble particles by anysuitable method. For example,

the resin-wax mixture may be melted and the water-soluble bodies stirredinto the mixture, separated and allowed to cool. However, the mosteffective method of application of the coating involves treating theparticles in a curtain coater. This method of coating the material isdescribed in detail in companion application Ser. No. 400,561. A briefdescription of the process is as follows: the molten resin-wax mixtureis discharged in an unbroken substantially rectangular vertical curtainand the Water-soluble particles in the form of pellets, etc. areprojected in a trajectory through the thin film or curtain that has beenformed; the particle is allowed toremain in the trajectory after passingthrough the curtain for a sufficient time for the coating to solidify.The particles then follow through a collecting surface. The coating issupplied in one or more passes of the particles through the coater.Thus, several passes are often re quired to attain a sufficiently solidcoating upon the particles. In general, viscosity of the wax-resinousmixture will be in the range of from 1002,000,000 cps. at 200 F.

A wide variety of forms of particles can be employed to produce theslow-release materials of this invention.

Y For example, the particles may be crystalline, granular,

in flake form, plus pellets, etc. In general, forms that aresubstantially spherical in shape will be easier to coat. The preferredsize of particles are those that will pass through a 4 mesh screen, butwill not pass through a 12 mesh.

The plant nutrients that are employed will in general be composed ofnitrogen, phosphorous, or potassium; but may include other minorconstituent materials. Examples of fertilizers which may be so employedinclude ammonium nitrate, ammonium sulphate, ammonium phosphate, urea,sodium nitrate, potassium nitrate, calcium nitrate, super-phosphate,dicalcium phosphate, basic calcium phosphate, potassium phosphate andpotassium chloride. Also, various blends of these special compounds maybe used, for example the mixed fertilizers which are in wide commercialuse may also be coated. Examples of other materials which may beimproved by the use of the coatings of this invention include the weedkillers such as sodium pentachlorophenate pellets and rock salt.

The following examples demonstrate the effectiveness of the coatingmaterials of this invention in reducing the rate of leaching by water.The wax employed in the examples.

nitrogen base fertilizer having a particle size of from A to A4". Thewax-polymer coating was applied by passing the fertilizer pelletsthrough the curtain-coater. 1 to 3 passes were employed. Table I,following, shows the amount of fertilizer leached from the coatedpellets. In each test, grams of coated fertilizer were charged to eachtube. The fertilizer was mixed with a composite soil sample and placedin a 1" diameter tube. The material was leached by successiveapplications of 150ml. portions of water. Each application roughlycorresponds to irrigation with one foot of Water. The time required forcompletion of the test was about four months.

These data show that the 80% leaching level, the blends of wax and resinA are more than twice as effective as wax alone as coating agents. Thefertilizer coated with 15% of the wax-polymer A blend required more than14 times as much water to leach 60% of the soluble material as thatrequired by the uncoated fertilizer.

Additional data on the coating and leaching of material other thanfertilizer is included in the following table. The tests were run underthe same conditions as de- 10 scribed above. The following materialswere used:

(I) 11-8-4 analysis commercial fertilizer TABLE I.RATE OF EXTRACTION OFNUTRIENTS FROM COATED FERTILIZERS Percent Additive Coating GramsFertilizer Leached After (60. distilled water)- ax t.,

Type Percent Percent 150 300 455 600 750 900 1,050 1,200 1,350 1,5001,650 1,800 1,950 2,100 (a) 25 4. 54 0.19 3. 33 4.16 4 0 5.17 5. 68 6.146. 46 6. 84 7. 7. 37 7.50 7. 60 7. 67 (a) 7.93 0 74 1.63 1.86 2.1 2.322.67 3.34 3.77 4.47 5.48 5.88 6.32 6.72 6.93 (a) 25 13.8 0. 62 0.89 1.01 1.1 8 1. 20 1. 1,. 41 1. 1. 76 2. 25 2. 65 3. 06 3. 28 3.53 (a) 15 4.28 5. 64 8. 02 8. 30 3. 33 8. 39 8. 47 8. 51 s. 45 8. 28 8. 25 8. 25 8.26 8. 29 8. 29 (a) 15 8.4 4. 33 6. 89 7. 28 7. 49 7. 57 7. 66 7. 73 7.72 7. 61 7. 60 7. 60 7. 61 7. 62 7. 61 (a) 15 13. 28 0. 82 3. 81 4. 454. 84 5. 05 5. 26 5. 47 5.62 5. 90 6.18 6. 34 6. 43 6. 48 6. 55 (b) 257.19 0.18 2. 26 2. 91 3. 32 3. 65 4.14 4. 66 5. 23 5. 6. 55 6. 65 6. 746. 86 6. 90 (b) 25 13.07 0. 00 1.10 1. 45 1. 65 1. 79 1. 93 2.11 2. 262. 3 3.17 3. 44 3. 69 3. 92 4. 06 (b) 15 5.14 1. 09 5.10 5. 95 6. 42 6.67 6. 90 7.10 7. 21 7. 34 7. 41 7. 46 7. 48 7. 51 7. 52 (b) 15 14.37 0.11 1. 66 2. 20 2. 59 2. 88 3. 22 3. 52 3. 79 4.09 4. 42 4. 69 4. 86 5.03 5.17 0 0 5. 71 9. 29 9. 91 9. 94 9. 99 10.08 10.20 10.24 10.07 10.1010.11 10.13 10.16 10. 18

As shown by the data of the above table, the waxgg fi s s sodlumPentachlorophenate Weed kluer polymer blends are extremely effective inreducing the c S amount of loss by leaching. Plotting the cumulative 30The coatings were applied by the technique of curtain amount offertilizer leached against the volume of leachcoating as describedabove. Coating A is a mixture of ing water yield significant results.This plot is shown in 70% of the 160/165 wax employed in the previoustests Table II. In deriving the data for the table, it was assumed with30% of the ethylene-ethylacrylate copolymer also that 10.69 grams of thematerial constituted 100% of the previously employed. Coating B is amixture of 70% of soluble constituents of the fertilizer, and on thisbasis 35 the wax with 30% polyethylene.

TABLE III.GRAMS OF MATERIAL LEACHED FROM WAX-POLYMER COATED PELLETSCumulative Amount of Water Used, ml.

Material Coating Amount of Coated Type Coating, Combined Wt. PercentResults, 450 600 750 900 1, 050 1, 200 1, 350 1, 500 1, 650

150 and 300 9. 3868 5558 4219 3877 3360 2889 2542 3087 2663 2281 9. 77374455 1678 1551 0848 0526 0820 0434 0250 0256 15. 3128 5746 6746 30682363 1813 1326 0873 0691 0441 A 12. O5 3. 0484 5505 7301 7422 5406 87268460 3532 3587 1462 A 28. 79 1639 1928 2760 2747 2836 3878 5208 32753887 2239 A 16. 12 6. 6510 1. 1926 1. 4132 9066 5676 8854 8589 2953 32801669 B 11. 94 6. 3917 7335 4224 2845 1953 2201 2613 2128 2096 1366 B 15.49 3. 9742 7575 5983 3994 2737 3497 3648 2007 2191 0974 B 18. 60 89785030 5632 5550 3865 5856 6630 3133 2653 1099 B 10. 13 5. 8391 1. 37438292 4664 2696 1704 1418 .1034 1363 0444 B 25. 22 4. 8558 8999 1. 21006506 3876 6154 6930 2369 3926 1808 Material Coating Amount of CumulativeAmount of Water Used, ml.

Coated Type Coating, Wt.

Percent 1, 800 2, 250 2, 400 2, 550 2, 700 2, 850 3, 000 Totals 18300600 0223 0258 0241 0342 0121 13. 0063 0161 0195 0056 0105 0013 01830014 10. 9624 0236 0175 0166 0354 0163 00321 0214 17. 8394 1292 09,600998 0967 0544 0749 0668 9. 1811 1719 1434 1755 1484 0987 0960 1016 4.3937 2138 1210 1341 0824 0990 0966 0791 14. 4335 1220 c 9. 1898 0922 4 4c 7. 3270 0926 0648 0750 1113 0270 0425 0326 5. 4792 0342 c a 9. 40911352 1288 0905 0901 0876 0722 0532 0375 10. 9828 the amount of waterrequired to remove various percentages of soluble fertilizer was readfrom the table.

TABLE II.-VOLUME OF WATER TO LEACH GIVEN PERCENT (ASSUMING 10.69g.=100%) (ml.)

Coating Percent Uncoated 2.5% Wax- 200 2.5% Wax, 210 5.0% Wax... 2005.0% Wax, A 260 10% Wax, A 300 15.0% Wax, A 1, 400

5 6 3. The material of claim 1 wherein said coating 'com- 3,223,51812/1965 Hansen 71-64 prises from 5 to 15% by weight of said material.3,232,895 2/1966 Klein et a1. 10 6230 References Cited DONALL H.SYLVESTER, Primary Examiner. UNITED STATES PATENTS 5 R. BAJEFSKY,Assistant Examiner.

3,288,587 11/1966 Campbell et a1 71-64

1. AS A SLOW-RELEASE AMTERIAL, A WATER-SOLUBLE PARTICULATE BODY HAVING AUNIFORMLY DISTRIBUTED COATING ON SAID BODY COMPRISING A MIXTURE OF FROM25 TO 95% BY WEIGHT OF A WAX AND FROM 5 TO 75% BY WEIGHT OF A COPOLYMEROF EHTYLENE AND VINYL ACETATE, AND WHEREIN SAID COATING COMPRISES FROM 2TO 25% BY WEIGHT OF SAID MATERIAL.